# Lemonade Change Problem

## Description

LeetCode Problem 860.

At a lemonade stand, each lemonade costs $5. Customers are standing in a queue to buy from you, and order one at a time (in the order specified by bills). Each customer will only buy one lemonade and pay with either a $5, $10, or $20 bill. You must provide the correct change to each customer so that the net transaction is that the customer pays $5.

Note that you don’t have any change in hand at first.

Given an integer array bills where bills[i] is the bill the i^th customer pays, return true if you can provide every customer with correct change, or false otherwise.

Example 1:

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Input: bills = [5,5,5,10,20]
Output: true
Explanation:
From the first 3 customers, we collect three $5 bills in order.
From the fourth customer, we collect a $10 bill and give back a $5.
From the fifth customer, we give a $10 bill and a $5 bill.
Since all customers got correct change, we output true.

Example 2:

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Input: bills = [5,5,10,10,20]
Output: false
Explanation:
From the first two customers in order, we collect two $5 bills.
For the next two customers in order, we collect a $10 bill and give back a $5 bill.
For the last customer, we can not give change of $15 back because we only have two $10 bills.
Since not every customer received correct change, the answer is false.

Example 3:

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Input: bills = [5,5,10]
Output: true

Example 4:

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Input: bills = [10,10]
Output: false

Constraints:

- 1 <= bills.length <= 10^5
- bills[i] is either 5, 10, or 20.

## Sample C++ Code

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class Solution {
public:
bool lemonadeChange(vector<int>& bills) {
int five = 0;
int ten = 0;
for (int i = 0 ; i < bills.size() ; i++) {
if (bills[i] == 5)
five++;
if (bills[i] == 10)
ten++, five--;
if (bills[i] == 20) {
if (ten)
ten--, five--;
else
five -= 3;
}
if (five < 0)
return false;
}
return true;
}
};